The long-range goal is to understand how the neural mechanisms for pursuit and saccadic eye movements operate in health and in various human disease states and how these mechanisms are related to visual perception. Recently, we have obtained behavioral and electrophysiological data indicating that there is functional overlap between the neural mechanisms for pursuit and saccades. The objective of this application is to investigate the nature and degree of this functional overlap In particular, we will determine how the rostral superior colliculus and one of its primary targets, the paramedian pontine reticular formation, participate in the control of pursuit, as well as saccades. This proposal tests two main hypotheses. First, that some neurons in the rostral superior colliculus encode the retinal locations of possible targets, rather than specific commands for eye movements. Second, that the decision to make a saccade or pursuit or no eye movement occurs downstream. The project will address the following three questions: (1) What types of information are encoded by neurons in the rostral superior colliculus that could be used to guide both pursuit and saccades? (2) Is activity in the rostral colliculus selective for the location of the target or the type of eye movement that the subject makes? (3) Could activity in the paramedian pontine reticular formation provide part of the command for pursuit or determine which type of eye movement is made? At the completion of this research, we expect to understand how activity in the rostral superior colliculus is related to the mechanisms of both target and eye movement selection, and to have a preliminary understanding of how activity in the paramedian pontine reticular formation contributes to the control of pursuit. These studies are a step toward understanding how the brain coordinates the components of voluntary movements and how it establishes and regulates the line between visual processing and movement selection. These studies will therefore help refine clinical descriptions of the oculomotor system that are used to diagnose eye movement disorders in humans.